1. Field of the Invention
The present invention relates to a process for producing a thermally developable light-sensitive composition, more particularly, to a process for producing a light-sensitive composition capable of providing a thermally developable light-sensitive element having reduced light discoloration after processing. The present invention also relates to thermally developable light-sensitive composition and elements.
2. Description of the Prior Art
A thermally developable light-sensitive element is known which utilizes a composition essentially comprising the silver salt of an organic acid, a small amount of silver halide, and a reducing agent, as described in U.S. Pat. Nos. 3,125,904 and 3,457,075. In this light-sensitive system, the silver halide that remains after development in the element is not stabilized against light, but allowed to discolor by light. The light-sensitive element is stable at ordinary temperatures, but when it is exposed in an image-wise pattern and heated, usually to above 80.degree. C., preferably above 100.degree. C., the organic silver salt oxidizing agent and the reducing agent contained in the light-sensitive layer undergo an oxidation-reduction reaction due to the catalytic action of the exposed silver halide existing in the vicinity thereof to form silver. By this reaction the exposed areas of the light-sensitive layer are rapidly blackened so that contrast is formed between exposed areas and unexposed areas (background), that is, an image is formed.
It is known that the thus formed image of such a thermally developable light-sensitive element becomes obscure because of undesired discoloration generated after development in unexposed areas (hereinafter referred to as light discoloration).
Among known methods of preventing such light discoloration there is one using a precursor of stabilizers such as azole thioethers and blocked azole thiones, such as described in U.S. Pat. No. 3,839,041; one using tetrazolylthio compounds, such as described in U.S. Pat. No. 3,700,457; and one using a light-sensitive halogen-containing organic oxidizing agent, such as described in U.S. Pat. No. 3,707,377.
It has been found, however, that light discoloration is not greatly decreased by the above methods.
In another method of solving the problem, the element is subjected to blueing by the use of a blue dye such as Victoria Blue, which results in an improvement of its whiteness. This method, however, provides no fundamental solution to the problem since the method simply gives the appearance of reduced discoloration to the element which still essentially undergoes light discoloration.